Derivative financial instruments - Schedule of notional quantities of commodity contract derivatives by type (Details) £ in Millions |
12 Months Ended | |
|---|---|---|
|
Mar. 31, 2024
GBP (£)
GWh
MMBTU
|
Mar. 31, 2023
GBP (£)
MMBTU
GWh
|
|
| Forward purchases of gas | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative non-monetary notional amount | 38,000,000 | 22 |
| Derivative term | 1 year | 1 year |
| Derivative contractual amount | £ | £ 14 | £ 24 |
| Electricity swaps | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative non-monetary notional amount | GWh | 14,128,000,000 | 14,076 |
| Gas swaps | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative non-monetary notional amount | 44,000,000 | 50 |
| Gas options | ||
| Disclosure of detailed information about financial instruments [line items] | ||
| Derivative non-monetary notional amount | 78,000,000 | 57 |